1. Field of the Invention
The present invention relates to a process for extracting or disposing of ammonia or ammonia compounds that occur during combustion processes and subsequent gas cooling and/or gas scrubbing.
2. Description of the Prior Art
During the treatment of exhaust gases that result from combustion processes, in order to reduce the concentration of nitrous oxide, either ammonia is added to the flow of gas ahead of a reduction (SCR process) or else ammonia or a substance that forms ammonia under the effects of temperature (e.g., urea, ammonium carbonate) is sprayed into the gas flow at a temperature range that is above 700.degree. C. (SNCR process). In both cases, some of the ammonia will not be used up during the process that reduces the NO.sub.x and will be carried out in the exhaust gases in the form of so-called ammonia slip [Ammoniakschlupf--Tr.]. This contaminates not only the atmosphere, but also any subsequent exhaust gas scrubbing systems, if ammonia or ammonia compounds (ammonium chloride, ammonium sulfate, ammonium bisulfite) are flushed out with the dust from a filter system.
It is true that the ammonium salts, which are formed in the exhaust-gas section at temperatures in excess of 300.degree. C., can be removed effectively with cloth filters; however, problems are encountered when such filter dusts are subjected to further processing. These problems lie in the fact that the filter dust is dampened with water in order to make it easier to handle. When this is done, the ammonium salts give up their ammonia, which then escapes into the atmosphere. In order to prevent this uncontrolled escape of ammonia, which can also occur during subsequent dumping, according to the state of the art, the filter dusts can now be subjected to a stripping process in which the ammonia is to a large extent driven off. However, during this stripping process, the filter dust is heated with steam or electrically, and subsequently moistened, which means that in addition, heavy metals and their compounds, in particular mercury, can escape in the form of gas, which leads to further environmental problems.